Speaker
Description
Tracking detectors in future high-energy and high-luminosity hadron colliders are required to correctly assign the tracks associated to the hard-scattering vertex among a huge number of pile-up vertices.
A detector with high spatial and timing resolution can remove pile-up tracks using the time information, enabling high-quality track reconstruction.
Capacitive Coupled Low Gain Avalanche Diodes (AC-LGAD) are semiconductor detectors that have high spatial resolution $\mathcal{O}(10)\ \mathrm{\mu m}$ and high timing resolution $\mathcal{O}(10)\ \mathrm{ps}$ .
However, LGAD does not have the radiation tolerance of $\mathcal{O}(10^{16})\ \mathrm{n_{eq}/cm^2}$ required for use as track detectors in future high-luminosity hadron accelerator experiments.
This is because, in addition to conventional semiconductor detectors, radiation damage in LGAD has a problem of acceptor removal, in which the p+ layer unique to LGAD, which is doped to provide a gain layer, no longer functional as an acceptor due to radiation damage.
The microscopic mechanism of acceptor removal is known to be that boron in the p+ layer, which has been inactivated by radiation damage, combines with oxygen in the sensor to generate $\rm{B_iO_i}$, which acts as a donor.
To understand and suppress acceptor removal, KEK and University of Tsukuba, in collaboration with Hamamatsu Photonics K.K. (HPK), have developed LGAD samples with various types of a gain layer as well as different wafer types. Especially to test the effect of oxygen concentration, radiation tolerance coefficients are compared among the samples with different oxygen concentration types and the Partially Activated Boron method which removes oxygen in the sensor by implanting more inactive boron than in normal samples.
We conduct proton irradiation experiments on these prototypes to evaluate their radiation tolerance by time resolution and IV measurements.
In this presentation, we will talk about the radiation tolerance measurement results for the prototype samples with various improvement and understanding of microscopic mechanism of acceptor removal then discuss possible further improvements.
